Field of the Invention
The present invention relates to a power storage system in which a plurality of battery packs are connected in parallel, and a power source system which is provided with the power storage system.
Description of the Conventional Art
Making a capacity of the power storage device large can be achieved by connecting a plurality of battery packs in parallel. However, in some voltage difference between the battery packs connected in parallel, great inrush current (cross current) flows from the battery pack having a higher terminal voltage toward the battery pack having a lower terminal voltage in the instant of connecting in parallel. The cross current causes a system down, for example, it brings about an abnormal state such as an over current and an over heat of the battery pack. As a result, there can be thought that the cross current is intended to be prevented by providing a charge switch and a discharge switch in each of the battery packs, and controlling the switches.
The cross current mentioned above is generated at the first starting time after the power storage device is installed, at the returning time from a long time stop or a fault, and at the replacing time of the partial battery pack.
As a countermeasure for preventing the cross current, there has been proposed a method of preventing the great cross current from being generated, by detecting the terminal voltage of each of the battery packs, and operating only the battery packs within a predetermined range of voltage difference in a state in which the battery packs can be charged and discharged in parallel.